This invention relates to polyurethane foam which can be densified and thermally re-expanded.
Polyurethane foams of various types are well-known and used for a variety of applications, including thermal insulation, packaging, padding, seat cushions, bedding, and the like. As with many low density materials, it is usually desirable to prepare the foam relatively close to the place where it will be used, since the foam takes up a large amount of space per unit weight. Because of this low density, transportation costs per unit weight are very high, and to avoid these costs it is desirable to minimize shipping the foam.
One way to reduce the shipping costs of flexible foam is to compress it for shipping, and permitting it to re-expand upon unloading. In this way, a greater weight of foam can be loaded into a given transport vehicle. However, many foams have a substantial compression set, and thus do not completely regain their original dimensions after unloading. In addition, because the compressed foams tend to re-expand, force must continuously be applied against the foam during loading and unloading procedures. The expansive force of the foam also tends to limit the amount of foam which can be packed into a given container, as the walls of the container must be of sufficient strength to withstand those forces. It would therefore be desirable to provide a polyurethane foam which can be easily transported at a relatively high density.